Method of making curved electrostatic printing screens



March 12, 1968 1 w, EDWARDS 3,372,639

METHOD OF MAKING CURVED ELECTROSTATIC PRI NTING SCREENS .Filed June 11, 1965 5 Sheets-$heet 1 INVENTOR JAMES W. EDWARDS ATTORNEY March 12, 1968 J. w. EDWARDS METHOD OF MAKING CURVED ELECTROSTATIC PRINTING SCREENS 5 Sheets-Sheet 2 Filed June 11', 1965 FIG.9

. INVENTOR JAMES W. EDWARDS ATTORNEY. .3

March 12, 1968 J. w. EDWARDS 3,372,639

METHOD OF MAKING CURVED ELECTROSTATIC PRINTING SCREENS Filed June 11, 1965 3 Sheets-Sheet 3 INVENTOR JAMES w. EDWARDS wwww ATTORNEY United States Patent Ofiiice 3,372,639 Patented Mar. 12, 1968 3,372,639 METHOD OF MAKING CURVED ELECTROSTATIC PRINTING SCREENS James W. Edwards, Creve Coeur, Mo., assignor to Monsanto Company, St. Louis, Mo., a corporation of Delaware Filed June 11, 1965, Ser. No. 463,251 4 Claims. (Cl. 101-1283) the printing element and the subject material being printed.

This technique involves the transfer of a liquid based ink or a resinous based ink through an electrostatic field to an image-receiving media. The ink or pigments are usually in the form of a fine powder having a particle size which is small enough to pass through the interstices of the open areas of a stencil or so-called screen. A roller or similar mechanical device normally carries the ink particles to a point in close proximity to the stencil and where the ink is carried through the stencil by the electrostatic field to the image-receiving media. When the voltage is applied to the roller or element carrying the pigment, the particles acquire a charge. The charge is, of course, opposite to the backing plate and the ink particles are, therefore, accelerated through the openings or interstices in the open areas of the screen and toward the image-receiving media. The image-receiving media may consist of a mandrel which serves as a counterelectrode and which is capable of retaining the article to be printed. Thereafter, the pigment will collide with and adhere to the article which is to be printed and the image is subsequently fixed by heat or solvent or a vapor or by other suitable means which are known in the prior art.

Since the initial development of the concept of elec trostatic printing, there have been many attempts to print by electrostatic process principles on items having curvilinear shapes. Most of these attempts proved to be unsuccessful, for a number of reasons. In all of the electrostatic screen process printing apparatus thus far developed, the apparatus has necessitated the transfer of ink across a definite and appreciable space. However with curved articles, all portions of the screen were not equidistantly spaced from the surface of the article to be printed. As a result thereof, the printing was weak in some areas and extra heavy in other areas. Furthermore, because of this variable spacing between the screen and the substrate to be printed the problems of ghosting effects arose.

It has recently been discovered that it is possible to print curvilinearly shaped articles by use of electrostatic screen process printing techniques by the employment of a curved screen. It was recognized that it is necessary to employ a screen having substantially the same size, shape and contour of the article being printed, in the areas where the article is to receive the print. However, to date, there has been no known method of producing an electrostatic screen having a curvilinear shape which can be employed in electrostatic process printing techniques. Accordingly, for this new technique recently developed, it was necessary to produce the screens by handmade operations. Because of the considerable labor involved, the

screens were naturally quite costly and moreover, they were not constructed to the desired degree of tolerance and perfection usually required in electrostatic screen process printing techniques.

It is, therefore, the primary object of the present invention to provide a method of making electrostatic screens for use in electrostatic screen process printing techniques.

It is another object of the present invention to provide a method of the type stated for producing electrostatic screens having curvilinear shapes.

It is a further object of the present invention to provide a method for producing electrostatic screens of the type stated which requires a minimum amount of manual attention and thereby permits construction of a low cost electrostatic screen.

It is also an object of the present invention to provide a method of making electrostatic printing screens of the type stated which can be used in the printing of articles having curvilinear shapes.

It is an additional object of the present invention to provide a method for producing screens of the type stated, where the screens are characterized by simplicity, dependability, ruggedness and low cost.

With the above and other objects in view, my invention resides in the novel features of form, construction, arrangement and combination of parts presently described and pointed out.

In the accompanying drawings (3 sheets):

FIGURE 1 is a perspective view of a wire mesh screen coated with an emulsion and used in the manufacture of the electrostatic printing screen of the present invention;

FIGURE 2 is a perspective View showing the method of forming a desired image on the wire mesh screen of FIGURE 1 where the image is projected through a negative having the desired pattern by means of the source of light;

FIGURE 3 is a perspective view of a hardening bath showing the wire mesh screen of FIGURE 2 submerged therein;

FIGURE 4 is a perspective view of a wire mesh screen of FIGURE 1 showing the emulsion removed from the non-printing areas;

FIGURE 5 is a perspective view of an electroplating tank showing the method of electroplating the wire mesh screen of FIGURE 4;

FIGURE 6 is a perspective view of a wire mesh screen showing the electroplating on the non-printing areas;

FIGURE 7 is a perspective view of an emulsion remover tank showing the wire mesh screen of FIGURE 6 submerged therein;

FIGURE 8 is a perspective view of a flat screen having a desired image printed thereon;

FIGURE 9 is a fragmentary sectional view taken along line 9-9 of FIGURE 8 and showing the construction of the printing areas on the screen of FIGURE 8;

FIGURE 10 is a perspective view of the flat screen of FIGURE 8 formed into a curvilinear shape;

FIGURE 11 is a perspective view showing an alternate process of forming an electrostatic printing screen where a mask having the desired image shape is applied to the surface of a non-metallic fabric;

FIGURE 12 is a side elevational view, partially in section of a metalizing tank for metalizing the screen of FIGURE 11;

' FIGURE 13 is a perspective view of an electroplating tank showing the screen of FIGURE 12 submerged therein for metalizing the non-printing areas;

FIGURE 14 is a perspective view of the flat screen showing the desired image produced thereon by the alternate process of the present invention;

FIGURE 15 is a fragmentary Sectional view taken along line 15-15 of FIGURE 14 showing the construction of the flat screen; and

FIGURE 16 is a perspective view of the screen of FIGURE 14 formed into a curvilinear shape.

Generally speaking, the present invention provides a process for producing curved screens to be used in electrostatic printing operations. Generally, the curved screens are of the type described in copending application Se No. 463,109, filed June 11, 1965, which relates to electrostatic screen process printing on curvilinearly shaped articles. In the process of the present invention, a direct screen photosensitive emulsion is applied to a wire mesh held in a screen chase. The screen is then exposed to light through a photographic negative of the required print or design which is ultimately to be produced on a substrate. The wire mesh is thereafter washed for removal of the unexposed emulsion, thereby leaving a positive image on the screen. The positive image is thereafter converted to a negative image required for printing by an electroplating operation. The electroplating device plates preferentially to the open mesh portions of the wire mesh. The screen is thereafter Subjected to an emulsion remover where the emulsion remover clears the printing areas thereby leaving a negative screen in which the non-printing areas have interstices filled with metal. The metalized screen is then formable through a desired shape by rolling, drawing or any other conventional metal forming process.

As an alternative to the present invention, a print is applied to a non-metallic mesh or fabric. The non-metallic mesh is preferably mounted in a frame during the processing operation and is coated with a direct screen photosensitive emulsion. A solid mask having an open area with the contour of the desired printing image is thereafter suitably applied to the surface of the fabric. The screen is then exposed to a suitable source of light where the exposed portions of the emulsion will harden and are removable in a subsequent emulsion removing operation. The mesh is thereafter metalized by any conventional process such as metal vapor deposition and the printing areas are washed with an emulsion remover. The positive image thus far produced is thereafter converted to a negative image to be used in the electrostatic printing by an electroplating operation. Again, the electroplating creates a plating preferentially to the open mesh portions of the fabric. A special electrode is designed to cover the entire back area of the screen and the screen is held to the electrode by a foamed plastic. The screen is thereafter shaped to a desired form by any mechanical process such as rolling, drawing or any similar metal forming process.

Detailed description Referring now in more detail and by reference characters to the drawings which illustrate practical embodiments of the present invention, the process of the present invention and the electrostatic screens produced thereby are more fully illustrated in detail. In FIGURE 1, a metal fabric or so-called wire mesh 1 is illustrated and may be suitably maintained in a retaining frame (not shown) if desired for processing. The metal fabric may be of the plain weave or the twill weave. However, in either weaves the openings are square. For the purposes of electrostatic screen process printing, the metal fabric should be formed of a No. 80-No. 350 wire mesh. However, in unusual cases coarser cloths than N0. 80 may be employed and similarly in unusual cases finer cloths than No. 350 may be employed. The wire mesh number is the standard employed in the metal fabric industry where for example No. 80 square mesh cloth would have 80x80 openings per square inch or 6,400 openings per square inch while No. 300 metal cloth would have 90,000 openings per tit) square inch. The wire mesh 1 may be formed of any suitable metal which has the desired gauge size and which is electrically conductive, at least for purposes of electrostatic printing. An electrostatic field is generally maintained between a screen and a counter-electrode. Such suitable metals to be used are nickel, copper, etc. Similarly, suitable alloys of metals may be employed such as stainless steel or a copper zinc alloy, etc.

A suitable direct screen emulsion or sensitized photographic coating is applied directly to the surface of the metal fabric 1. The coating may be applied in the liquid state by brushing, spraying, rolling or any other suitable technique. Thereafter, the coating is allowed to dry completely, usually 15 to 30 minutes at room temperature. Sensitized photographic coatings such as polyvinyl alcohol, polyvinyl acetate, modified polyvinyl plastics, commercial coatings, gelatinous coatings, transfer-type sensitized films and knife-cut films may be deposited on the metal screen fabrics. The important step before the application of the sensitized coating is to insure that the metal fabric is cleaned perfectly. Since the metal is nonabsorbent, it is essential that the fabric be clean and devoid of any oils or greases in order that the emulsion film or coating used is well adhered to the surface of the wire mesh 1. Generally, the metal fabric 1 may be cleaned by washing the same in a 5 to 10% glacial acetic acid solution for approximately 5 to 10 minutes and then rinsed well with hot water. The formulas for sensitizers may vary considerably and the most desirable type of sensitizer must be selected. One of the most efficient sensitizers found for use in the present invention contains ammonium bichromate, potassium bichromate, ammonium hydroxide, glycerin solution, and distilled water.

The metal fabric is then exposed to a proper light source through a photographic negative of the required print or design, such as FIGURE 2. It can thus be seen by reference to FIGURE 2 that the metal fabric 1 is exposed to a proper white-light source 2 through a negative 3 having the proper design which is to be formed on the metal fabric 1 such as illustrated by reference numeral 4. The sensitized metal fabric 1 may be exposed in either a dry or damp state depending on the type of screen that is being prepared. The length of the exposure is determined by experimentation but may vary anywhere from about 5 to 20 minutes depending on different factors. The type of light employed for exposing is very important and must be uniform in actinic inten sity. In other words, the light energy should produce uniform chemical change in all areas during all times that the light is on. Generally, conventional photo-flood lamps and are lamps provide suitable results.

After the sensitized metal fabric 1 has been exposed to the light source 2, it is then developed or hardened in a developing tank 5 substantially as shown in FIG- URE 3. Development generally takes place in hot water with a temperature within the range of to F. The water preferentially washes away or dissolves all of the unexposed portions of the photosensitive emulsions. The portion of the emulsion not residing in the image pattern 4 and which has been exposed to light becomes hardened and is now impervious to the wash treatment and remains on the metal fabric 1. The tank 5 is preferably made of glass, Bakelite, stainless steel, or a tank which is porcelain finished on the interior surface. The tank 5 may be rocked gently creating movement of the water to provide some slight agitation. FIG- URE 4 illustrates the metal fabric 1 after the development in the tank 5 with the positive image 4 on the surface thereof.

The positive image is then converted to a negative image which is necessary for electrostatic printing by electroplating or any similar process depositing metal on the open mesh portions of the screen. FIGURE 5 illustrates an electroplating apparatus 6 in which the metal portions of the screen, the positive image 4 5 fabric 1 having the positive image 4 on its surface is suspended from an electrically conducting rod 7. The screen 1 as illustrated in FIGURE 4 has open mesh portions where the photosensitive emulsion was washed from the surface of the screen in the developing process. The electroplating will go preferentially to these open mesh portions of the screen. The apparatus for performing the electroplating operation is conventional in its construction and is therefore not described in detail herein. However, it should be understood that the metal fabric 1 can be coated in the open mesh areas with such metals as copper, nickel, silver, etc., which may be used in the electroplating operation. FIGURE 6 illustrates the construction of the metal fabric 1 having the negative image 4 on the surface thereof. It can thus be seen, that as the plating goes preferentially to the open mesh presented in FIGURE 4 has been converted to the negative image 4 as shown in FIGURE 6.

However, at this point it should be observed that the electroplating operation has not affected the emulsion which remains in the image portion 4 of the metal fabric 1. Accordingly, the metal fabric 1 is then immersed in an emulsion remover which is maintained in a tank 8 as illustrated in FIGURE 7. Again, the tank 8 may be formed of glass, Bakelite, stainless steel or any synthetic resin which may be inert to the emulsion remover contained therein. Any mild oxidizing agent such as hydrogen peroxide or weak solutions of sodium peroxide may be used for dissolving the emulsion in the image portion 4. FIGURE 8 illustrates the flat metal fabric which has been removed from the emulsion remover in the tank 8. Thus, it can be seen that after the electroplating operation and the emulsion removing operation, the image portion 4 provides an open mesh area where the areas not included in the image portion 4 are solid. Moreover, by virtue of the fact that the screen has metal particles contained within the interstices of the closed areas, such as illustrated in FIGURE 9, the screen provides a fairly rigid structure which may be metal formed in a conventional operation.

After the flat metal fabric 1 has been removed from the tank 8 it may be suitably washed as desired, for removal of any of the excess emulsion remover. Thereafter, the metal fabric 1 may be dried. After drying of the metal fabric 1, it can then be formed into any suitable shape. Inasmuch as the metal fabric is rigid, it is capable of being formed by such operations as rolling, drawing, pressing, etc. so as to be shaped into surfaces that will parallel complex surfaces to be printed. Thus, the metal fabric is formed into a suitable screen 9 as illustrated in FIGURE 10.

It has been found that screens of this type find particular utility for electrostatic printing in the apparatus described in copending application Ser. No. 463,109, filed June 11, 1965. In the apparatus and methods described in said copending application, an electrostatic screen 9 is disposed in a spaced relation to an electrode designed to hold a substrate. Generally, the substrate will have a curvilinear shape such as a conically shaped container. Furthermore, the counter-electrode is generally in the form of a mandrel which has the same size and shape as the container. Thus, the container is mounted on the mandrel in spaced relation to the screen 9. It has been .found that the electrostatic printing can be formed on curvilinear surfaces where the screen has a surface contour in at least one plane which is substantially identical to at least one portion of the surface contour of the element being printed. The screen is rotated or oscillated in timed relation to the rotation or oscillation of the element being printed. In this manner, the container tangentially approaches and tangentially departs from the screen so that printing will occur through the screen along an elemental line of closest approach. The container is generally rotated at approximately the same rate of speed as the rotation or oscillation of the screen through this line of closest approach so that a continiuing line of tangency occurs between the surface of the container and the surface of the screen. A desired electroscopic ink is spread through the screen along this line of closest approach by any suitable ink treating mechanism. Furthermore, by use of screens produced by the method of the present invention, it is possible to employ contact electrostatic printing on curvilinear surfaces. This method is again described in the aforementioned copending applica tion.

Any of a variety of electroscopic inks can be used where the screen produced by the present invention is used in the electrostatic printing operations. Generally, the electroscopic inks comprise a finely dispersed powder which is capable of being triboelectrically charged. The powder generally carries a desired pigment. A number of satisfactory powders can generally be employed in the electrostatic printing Operations and each must be in a finely divided state. Suitable powders are dyed thermoadhesive resins such as rosin, gum copal, gum sandarac, ethyl cellulose. Egyptian asphalt and the like. A very satisfactory thermoadhesive powder can be produced by dissolving equal parts of ethyl cellulose and Vinsol resin in acetone together with a small amount of spirit soluble aniline dye such as Nigrosine or aniline blue and spray drying the solution to produce an extremely fine powder having substantially spherical particles. Dyed Lycopodium powder is suitable where thermoadhesive properties are not required of the powder, as is also starch, cellulose flour, powdered metal and copper powder.

Whether fusible, thermoadhesive or non-fusible powders or others are used, the particle size is preferably near the limit of definition of the eye under ordinary reading conditions. Excessive powder size contributes to graininess in appearance of the image. On the other hand, extremely fine powder may be undesirable in many instances due to its tendency to ball up or cling together in clusters. It is, therefore, desirable to use a powder in which substantially all the particles are within the size range of 1 to 10 microns. If spherical powders are used, this refers to their diameters, otherwise to the largest dimension. For most purposes, it is preferred to use an equi-dimensional powder particle, the sphere being the preferred form.

As previously indicated, when the screen produced by the present invention is employed in an electrostatic printing operation, voltage is applied to the counter-electrode which holds the substrate, the screen and to a feeding electrode. The charge in the counter-electrode is opposite to the charge on the screen so the particles are propelled through the openings or interstices of the screen toward the counter-electrode. The image is then generally subsequently fixed by heat, a solvent, or a vapor, or by any other suitable means depending upon the type of pigment powder which has been employed and the nature of the material being printed.

The voltage source employed in electrostatic printing operations is adapted to develop a relatively high direct current potential. While the current requirements for electroprinting of the type here employed are not heavy in the ordinary sense, a very definite electron current or space current flows across the printing space during the printing operation. It is desirable to have a space current of at least 1 to 2 milliarnperes per square inch of printing area. Moreover, the high potential source should be capable of maintaining a desired voltage and current level in the range of approximately milliamperes or slightly more.

It should be recognized that the electrostatic screens produced by the present invention have the capabilities of withstanding this type of high voltage potential applied thereto. Moreover, they are capable of withstanding abrasion of the rough handling by virtue of their construction.

The present invention also provides an alternate methd of producing curvilinear electrostatic screens, which method is more fully illustrated in FIGURES ll16 inelusive. In the alternate process of the present invention, a nonmetallic fabric is employed. The fabric 1% is preferably removably mounted in a frame until the process of forming the fabric into a screen has been completed. In this case, the frame does not constitute a final part of the screen. Preferably, the frame should be made of wood or a suitable plastic or synthetic resin material which is not affected by emulsion removers, electroplating processes and the like. The fabrics which may be employed in the construction of an electrostatic screen are silk, organdy, cotton, nylon, Dacron, vinyl, vinyon, linen, etc. The fiber of the fabric may be made of animal, plant, mineral, synthetic material or combinations of the above materials. However, of all of the fabrics attempted for use, a synthetic cloth containing monofilament strands such as cloth sold under the trade name Nylon has been found to be the most suitable. The cloth fabrics employed may be a gauze weave, a leno weave, or a plain weave.

A suitable direct screen emulsion or sensitized photographic coating is applied directly to the surface of the fabric 10. Again, the coating may be applied in a liquid state, by brushing, by spraying, by rolling or any other suitable technique normally employed in applying coatings of this type. Thereafter, the coating is allowed to dry completely which usually requires to minutes at room temperature. The sensitized photographic coating such as polyvinyl alcohol, polyvinyl acetate, modified polyvinyl plastics, commercial coatings, gelatinous coatings, transfer-type sensitized film and knife-cut films may be deposited on the fabrics 10. Of course, it should be recognized that the fabric 10 must be chemically clean before the application of the coating. A mask 11 preferably formed of a non-metallic material Such as a polyvinylbutyral plastic is then placed upon the upper surface of the non-metallic fabric 10, and may be secured thereby by any suitable adhesive. However, it is not necessary to adhesively secure the mask 11 to the fabric 10, if the mask is only to remain during the photographing operation. The mask 11 is preferably solid and is designed to cover the entire fabric except that it is open in the desired image area and the open portion has the desired image or shape which is ultimately to be printed on a substrate. In this manner, only the image area will be exposed to light in a method hereinafter described in detail.

Th fabric 10 is then exposed to a proper light source which is sufficient to create a photochemical effect upon the photosensitive emulsion. In this embodiment, it is not necessary to employ a photographic negative of the desired image since the mask 11 takes the place of the negative. In effect, the creation of the image on the photosensitive emulsion deposited on the fabric 10 is more analogous to contact photographic printing. The sensitized fabric 10 may be exposed in either a dry state or a damp state and the length of exposure is determined by experimentation which may vary anywhere from about 5 to 25 minutes depending on different factors. Again, the type of light employed for exposure is very important and must be uniform in actinic intensity.

After the evposure of the sensitized fabric 10, the mask 11 is suitably removed. Generally, if the mask 11 is adhesively secured to the fabric 10, the adhesive employed is such that it will not destroy the fabric or in any way mar the surrounding emulsion when the mask 11 is removed. After the mask 11 has been removed, the sensitized non-metal fabric 10 is then developed in a developing tank similar to the tank 5 shown in FIGURE 3. Development generally takes place in hot water with a temperature within the range of 95 to 115 F. The water preferentially washes away or dissolves all of the unexposed portions of the photosensitive emulsion. Therefore, the fabric 1t is provided with an image area or image pattern 12 and a non-image area 13, the image pattern 12 of which has a hardened photosensitive emulsion deposited thereon. The non-image areas are then clear of the photosensitive emulsion. The tank in which the developing takes place should be agitated slightly to insure complete removal of all of the unexposed photosensitive emulsion, which resides in the image pattern 12. At this point, it can be seen that the image thus far created is a negative image.

The fabric 10 with the mask 11 removed therefrom is then metalized in a conventional metalizing chamber 14 such as the type shown schematically in FIGURE 12. In this type of chamber, the non-metallic fabric 10 is supported in upwardly spaced relation to a crucible .15 containing a desired metal 16. The crucible 15 is provided with electrical contacts 17 for connection to a suitable source of electrical current whereby the crucible 15 may be heated for vaporizing the metal 16. The vaporized metal 16 then strikes the fabric 19 from many angles and condenses on the mesh portion thereof. It is preferable to use a plurality of individual metalizing sources so that more than the undersurface of the fabric 10 will be coated. It is to be noted, however, that the metal will adhere to the entire surface of the fabric 10 including the portions with the hardened emulsion, that is in the image pattern 12 and will also adhere to the cloth fabric 10 in the non-printing areas 13. The metalizing operation serves to render the fabric 10 electrically conductive so that the fabric 10 can be electroplated in a desired manner. 7

It should be recognized that the metalizing operation performed, such as in the vacuum vapor deposition chamber, does not produce any rigidity in the screen. Accordingly, the fabric 10 is electroplated in a suitable electroplating apparatus 18, substantially as shown in FIGURE 13. The electroplating will go preferentially to the open mesh portions of the screen, that is the non-image areas 13. Inasmuch as the photosensitive emulsion still remains in the image pattern 12, the electrolyte or electroplating solution cannot pass through the open mesh portions of the fabric and hence this area will not become electroplated. In many cases, the image areas 12 may have portions which are to be electroplated but are not within conductive relationship to the remaining portions of the nonimage areas 13. Accordingly, the fabric 19 is mounted in conductive relationship upon an electrode or conducting plate 19 and is held or pressed thereto by a porous polyethylene body 20 with the metalized side toward the electrode 19. In this manner, all portions of the fabric 10 are at least in electrically conductive relationship to the conducting plate 1. Furthermore, the electroplating solution can flow through the porous polyethylene body 28 without interfering with the electroplating operation. The combination of the fabric 10, the plate 19 and the polyethylene body 21) is suitably connected to a support rod 21 by means of clips 22, substantially as shown in FIGURE 13. The remainder of the apparatus 18 for performing the electroplating operation is conventional in its construction and is, therefore, not described in detail herein. However, it should be understood that the same metals which were used in the electroplating apparatus 6 can also be used in the electroplating apparatus 18. FIGURE 14 illustrates the construction of the non-metal fabric which has been metalized in the electroplating operation and having the negative image 12 on the surface thereof. It can be seen that the plating goes preferentially to the open mesh portions of the screen. The positive image 12 therefore has been converted to the negative image 12 prior to the electroplating operation as shown in FIGURE 14. The construction of the screen having the metalized particles in the interstices of the non-metal fabric is more fully illustrated in FIGURE 15.

The non-metallic fabric 1%}, which has been metalized in the electroplating operation, is then immersed in an emulsion remover which is retained in a tank similar to the tank 8 shown in FIGURE 7. The emulsion remover may be any mild oxidizing agent, such as hydrogen peroxide, or weak solutions of sodium peroxide. The emulsion removers, which may be employed in the alternative process described herein, are the same as the emulsion removers in the first process described herein. The emulsion remover is designed to remove any remaining emulsion which may be residing in the image portion 12. Thus, it can be seen that after the electroplating operation and the emulsion removing operation, the image portion 12 provides an open mesh carrier where the areas not included in the image portion 13 are solid. Moreover, the screen thus produced presents a fairly rigid structure which may be metal formed in any conventional operation. If desired, the fabric 10 may be rinsed in a mild warm water solution for removal of any excess emulsion removed. After the drying of the fabric 10, it can then be formed in any suitable shape. Inasmuch as the fabric is rigid from the electroplating operation, it is capable of being formed by such operations as rolling, drawing, pressing, etc. so as to be shaped into surfaces that will parallel complex surfaces to be printed. Thus, the non-metallic fabric is thereafter formed into a suitable curved screen 23, substantially as shown in FIGURE 16.

The invention is further illustrated by but not limited to the following example.

Example A metallic fabric of Phosphor bronze having 200 mesh was suitably mounted in a retaining frame. A direct photosensitive emulsion of a type used in conventional screen process printing was thereafter applied to the wire mesh screen on both sides of the screen in a fairly heavy coating which was approximately 0.005 inch thick. The screen was then made into several smaller frames by securing brass rings to the screen with an epoxy cement. Thereafter, the various screen sections were subjected to experimental plating tests With copper, silver, cadmium and nickel. The nickel plating was slightly brittle and the silver plating was heavy but ductile enough for forming. The copper plating samples, however, appeared to give 0ptimum results.

The metallic fabric was then treated with an emulsion remover formed of concentrated nitric acid diluted in a 3:1 ratio with water. This treatment was performed several times. Thereafter the screen was scrubbed with hot water and a detergent between each emulsion removing operation. The screen was then formed into a curved surface so that it was capable of being used in printing on conically shaped containers.

It should be understood that changes and modifications may be made in the form, construction, arrangement and combination of parts presently described and pointed out without departing from the nature and principle of my invention.

Having thus described my invention what I desire to claim and secure by Letters Patent is:

1. The method of making electrostatic printing screens, said method comprising applying a photosensitive emulsion to the surface of an electrically non-conductive fabric, applying a mask of a desired print image to the surface having the photosensitive emulsion, exposing the emulsion to a source of light so that the portion not covered by masked areas receives light, removing the mask, removing the unexposed emulsion, metalizing the open areas of the fabric to render the fabric electrically conductive, metalizing the fabric in a second metalizing operation so that the metal is filled in the interstices of the open mesh portions of the fabric to provide a fairly rigid screen member, treating the screen member with an emulsion remover to convert the positive image to a negative image, and forming the screen member to a desired shape.

2. The method of claim 1 wherein the second metalizing operation is electroplating.

3. The method of claim 1 wherein the first metalizing operation is vacuum metal vapor deposition and the sec- 0nd metalizing operation is electroplating.

4. The method of claim 1 wherein the screen member is formed to a desired curvilinear shape.

References Cited UNITED STATES PATENTS 2,340,485 ,2/1944 Norris 10l-128.4 X 2,906,201 9/ 1959 Blair. 3,081,698 3/1963 Childress et al. 101129 1,064,166 9/1913 Pindikowsky 101-128.3 2,064,764 12/1936 Playford et al 101-1283 2,213,237 9/1940 Brennan et al. 101-1282 X FOREIGN PATENTS 420,125 11/1934 Great Britain. 457,496 11/ 1936 Great Britain.

DAVID KLEIN, Primary Examiner. 

1. THE METHOD OF MAKING ELECTROSTATIC PRINTING SCREENS SAID METHOD COMPRISING APPLYING A PHOTOSENSITIVE EMULSION TO THE SURFACE OF AN ELECTRICALLY NON-CONDUCTIVE FABRIC, APPLYING A MASK OF A DESIRED PRINT IMAGE TO THE SURFACE HAVING THE PHOTOSENSITIVE EMULSION, EXPOSING THE EMULSION TO A SOURCE OF LIGHT SO THAT THE PORTION NOT COVERED BY MASKED AREAS RECEIVES LIGHT REMOVING THE MASK, REMOVING THE UNEXPOSED EMULSION, METALIZING THE OPEN AREAS OF THE FABRIC TO RENDER THE FABRIC ELECTRICALLY CONDUCTIVE, METALIZING THE FABRIC IN A SECOND METALIZING OPERATION SO THAT THE METAL IS FILLED IN THE INTERSTICES OF THE OPEN MESH PORTIONS OF THE FABRIC TO PROVIDE A FAIRLY RIGID SCREEN MEMBER TREATING THE SCREEN MEMBER WITH AN EMULSION REMOVER TO CONVERT THE POSITIVE IMAGE TO A NEGATIVE IMAGE, AND FORMING THE SCREEN MEMBER TO A DESIRED SHAPE. 